Vague legislation no longer supporting case for intervention (7)

I believe the answer is:
inexact
'vague' is the definition.
(I've seen this before)
'longer supporting case for intervention' is the wordplay.
'longer' becomes 'exact' (I can't justify this - if you can you should believe this answer much more).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'case for' says to hollow out the word (remove centre letters) (the letters which encase the others are used).
'intervention' with its centre taken out is 'in'.
'exact' after 'in' is 'INEXACT'.
'legislation no' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for inexact that I've seen before include "Vague" , "Not quite right" , "Fuzzy, muddled" , "Woolly" , "loose" .)
